S34 



AMPHIBIA. 



processes, and a short neural spine. The eighth vertebra 

 has a biconcave or amphicoelous centrum. The ninth is 

 convex in front, with two convex tubercles behind, and 



bears large transverse pro- 

 mx cesses with which the hip- 



girdle articulates. The uro- 

 style, formed by the fusion 

 of several vertebras, has 

 anteriorly a dorsal arch 

 enclosing a prolongation of 

 the spinal cord ; but both 

 arch and nerve-cord soon 

 #/ disappear posteriorly. The 

 notochord, around which 

 the vertebral column has 

 developed, is finally repre- 

 sented only by the vestiges 

 in the centra of the vertebrae. 

 The skull consists — (a) of 

 the persistent parts of the 

 original cartilaginous brain- 

 box or chondrocranium, de- 

 veloped, as in the skate, from 

 parachordals and trabecular, 

 plus nasal and auditory 

 Fig. 227.— Skull of frog— upper and capsules ; (/>) of ossifications 



pJrker SUrfaCe ' - '^^ W ' K ' ° f P artS ° f the chondr °- 



' cranium, cartilage bones ; (c) 



Upper surface — c , ° . 7 . v ' 



Pmx., premaxiiia; n., nasal; m., ot membrane or investing 



bones; and (d) of associ- 

 ated visceral arches. 



maxilla; Sg., squamosal; Q.J.,, quad- 

 rato-jugal ; e.o., ex-occipitaI&; P.f. 

 parieto-frontals ; Sph.E., spheneth 

 moid ; P.O., pro-otic. 

 Lower surface — 

 Pmx. , premaxiiia ; M. , maxilla ; Q.J. 



quadrato-jugal ; Q., quadrate; Pt. 



pterygoid ; Ps., parasphenoid ; P.O. 



pro-otic ; Sp.E., sphenethmoid ; Pi. 



palatine ; V., vomer ;. c, columella. 



Two ex-occipitals bounding the 

 foramen magnum and forming the 

 condyles, two pro-otics or ossi- 

 fications of the original auditory 

 capsule, and an unpaired spheneth- 

 moid forming the front of the brain-case, are cartilage bones. Probably the 

 slender rods known as quadrato-jugals or jugals are also cartilage bones. 

 Two parieto-frontals and two nasals above, a paired vomer and an 

 unpaired dagger-shaped parasphenoid beneath, and two lateral hammer- 

 shaped squamosals aie membrane bones. There is no basisphenoid 

 ossification. 



